hive-agent-mcp, hive-c0re, hive-sh4re: drop agent param from get_loose_ends

get_loose_ends now always returns the caller's own loose ends, for every
caller including the manager (ruth) — there is no separate manager
surface, ruth is a normal agent with different default capabilities.

- AgentGetLooseEndsArgs removed; get_loose_ends takes no args.
- Wire Request::GetLooseEnds collapses from an Option<String> target to
  a unit variant.
- hive-c0re's handle_get_loose_ends drops the "*" hive-wide branch and
  the subtree/capability resolver (resolve_agent_state_target); both
  are gone since there is no longer a target to resolve.
- loose_ends::hive_wide and Capability::QueryAgentState removed as
  dead code — their only callers were the two functions above.
- is_descendant_of is untouched (still used by lifecycle_handlers.rs
  and schedules.rs independently of this change).
- Docs updated: docs/turn-loop/mcp.md, docs/web-ui/dashboard.md,
  docs/process/conventions.md (Loose-ends wire shape + capabilities
  table), plus the doc comments in hive-core-agent-sock, mcp_config.rs
  and capabilities.rs that described the old shape.

Refs #4480

hive-agent/src/main.rs

@@ -358,7 +358,7 @@ impl Surface for AgentSurface {
     async fn post_turn_counts(socket: &Path) -> (Option<u64>, Option<u64>) {
         let threads = match hive_sock_client::request::<_, Response>(
             socket,
-            &Request::GetLooseEnds { agent: None },
+            &Request::GetLooseEnds,
             CONTROL_SOCKET_RETRY,
         )
         .await

hive-agent/src/mcp_config.rs

@@ -49,12 +49,9 @@ fn allowed_capability_tools() -> Vec<String> {
         let t = token.trim().to_ascii_lowercase();
         match t.as_str() {
             "read_host_journal" => tools.push("get_host_journal".to_owned()),
-            // manage_root_agent / query_agent_state don't expose new MCP
-            // tools: manage_root_agent gates existing lifecycle tools via
-            // topology enforcement; query_agent_state unlocks the `agent`
-            // field in get_loose_ends / count_pending_reminders /
-            // reminder_rollup (c0re enforces the cap server-side).
-            "manage_root_agent" | "query_agent_state" => {}
+            // manage_root_agent doesn't expose a new MCP tool: it gates
+            // existing lifecycle tools via topology enforcement instead.
+            "manage_root_agent" => {}
             unknown => {
                 tracing::warn!(capability = %unknown, "unrecognised capability in HIVE_CAPABILITIES — skipped");
             }